If there is one teaching that is peculiar to Buddhism alone among all the world’s religions, I would say it is the principle of sunyata (Voidness or Emptiness). If I were to choose one doctrine among others that best represents the core of Buddhism, I would also choose the principle of sunyata. If someone were to further ask me what is the Buddhist doctrine that is most difficult to explain and comprehend, most misunderstood and misrepresented, I would again say it is the principle of sunyata. The importance of this remarkable Buddhist classic and its wide influence on Buddhist thought cannot be overstressed. This Sutra comprises only 262 words in the Chinese translation and can easily be printed on a single page. It is said, however, that the essence of the entire Mahayana teaching is contained therein. The text is both incredibly compact and pithy, and the reader should be alerted to its profuse and far-reaching implications.
Garma C.C. Chang, The Buddhist Teaching of Totality, p.64

“Form is emptiness, emptiness is form.” That is, form is form, emptiness is emptiness.
Shobogenzo, Maka-hannya-haramitsu, Hee-Jin Kim (Flowers of Emptiness, p.61)

According to Zen lore, the Sixth Ancestor realized enlightenment simply upon hearing the Diamond Sutra, being recited by a person in the street. Huineng’s record, the Platform Sutra, proclaims the supreme vision of the Diamond Sutra, promising enlightenment not only to those that put its teachings into practice, but even to those that simply memorize it. The central importance of emptiness in Buddhism can be seen in the Zen/Buddhist axioms, “All things are essentially empty,” and “Emptiness is the true nature of all things.”

The Buddhist doctrine of emptiness is multifaceted (i.e. ‘complex’ not ‘complicated’). The truth of any facet of the doctrine is dependent on its context in the complete form. To be ‘empty’, as in the Buddhist axiom, ‘All things are essentially empty,’ means to be empty of selfhood, to lack independent existence. To be empty does not mean to be unreal, illusory, or nonexistent, as is commonly misunderstood.

Historically, Zen/Buddhist students have demonstrated a propensity for giving rise to distorted notions of emptiness. Such distortions usually boil down to a privileging of emptiness (essence, nature) over and above the form (appearance, manifestation). Such privileging arises from and is maintained by the abstract speculation inherent to dualism. Briefly, the emptiness and form of dharmas are theoretically conceived of as two independent realities. Being regarded as two separate realities, emptiness and form become subject to comparative analysis and categorization. Naturally, the ‘reality’ of emptiness, which is conceived of as uniform, universal, and pure comes to be regarded as superior to the ‘reality’ of form, which is conceived of as variable, particular, and disparate. Such biased (one-sided) views have spawned distorted doctrines fostering pernicious practices of quietism, escapism, and detachment that have plagued Zen down to the present day.

Dogen’s writings, like many Zen records, frequently appeal to and apply the methodology of the Diamond Sutra to present the intrinsic nonduality of emptiness and form. The gist of the central methodology demonstrated by the Diamond Sutra can be expressed: form is not-form (i.e. form is empty), therefore form is form; emptiness is not-emptiness (i.e. emptiness is form), therefore emptiness is emptiness.

The basic reasoning here can be generally understood by envisioning ‘A’ as one particular dharma, and ‘not A’ as everything else throughout space and time. When we do this we can clearly see that to think of, speak about, or act on ‘A’ requires us to distinguish ‘A’ from everything that is ‘not A’ – thus, the existence of ‘A’ presupposes (i.e. depends on) the existence of ‘not A.’ By the same reasoning, the existence of ‘not A’ can be seen as presupposing the existence of ‘A.’

Here we come to the crucial point, since the existence of ‘A’ depends on the existence of ‘not A,’ ‘A’ is and must be inclusive of ‘not A.’ Thus we see that the whole of existence-time that is not explicit in/as ‘A’ is and must be implicit in/as ‘A.’ In other words, the whole reality of ‘A’ is constituted of both what is ‘A’ and what is ‘not A’ – which is to say that ‘A’ (and by extension, any and every particular dharma) is, as it is, a particular phenomenal appearance of the whole universe. This vision of the nondual nature of dharmas – their reality simultaneously consisting of particular, unique instances of/at specific location-moments and the totality of all location-moments – is most explicitly elucidated in Dogen’s works through his expressions concerning the ‘total exertion of a single dharma’ (ippo gujin).

Here it is worth touching on some of the implications exemplified by the methodology of the Diamond Sutra. The Zen practitioner that focuses attention on dharmas in accordance with this methodology is directly enlightened (i.e. clearly discerns and understands) to the truth that dharmas are dharmas by reason of their being particularities – that is, by their being some-thing differentiated from every-thing. Experiencing the world through the perspective enabled by applying the technique presented by the Diamond Sutra, the practitioner is made intimately aware of the fact that reality only and always consists of particular instances of total space-and-time – apart from specific manifest phenomena there is no space or time.

Thus, to (epistemologically) encounter (ontological) reality is only and always to distinguish something from everything. If something is not distinguished from everything, nothing can be encountered. By applying the methodology of the Diamond Sutra we first come to discern that the existence of any particular dharma is dependent on the existence of everything ‘other than’ that dharma; advancing further, we discern that the existence of everything ‘other than’ that dharma is dependent on the existence of that dharma. As our application continues to advance, we come to discern that each particular dharma inherently presupposes (contains, includes) everything ‘other than’ that particular dharma (and vice versa). Thus, it is also accurate to say that, to encounter a dharma is to distinguish everything from something.

In sum, the Diamond Sutra presents (makes present) the dynamic interdependence of form and emptiness by demonstrating that ‘A’ is essential to, therefore inclusive of ‘not-A’ (and vice versa). Thus, A is not-A, therefore A is A, or, in the terms applied by Shobogenzo; form is emptiness, emptiness is form, therefore form is form, emptiness is emptiness.

While the Diamond Sutra continues to be highly revered in Zen, which remains deeply steeped in its methodology, the concise Heart Sutra came to be regarded as the definitive statement on emptiness in Zen, as in other Mahayana traditions. The Heart Sutra, as the title suggests, expresses the heart (the essential core) of Buddhism’s insight into emptiness. The key phrase, “form is emptiness, emptiness is form,” is the Heart Sutra’s succinct crystallization of this insight.

In the earliest fascicle composed for Shobogenzo, Maka-hannya-haramitsu, Dogen employed the perspective provided by the Heart Sutra to illumine the reason (dori) of emptiness. This revered scripture was familiar enough by Dogen’s time (1200-1253) that he needed only cite its first line to indicate it as the perspective from which his commentary is addressed. The fact that he chose to alter that first line by adding a single word is significant. The very succinctness of the Heart Sutra makes Dogen’s slight alteration starkly apparent. The additional word initially jumps out as if misspoken; as its implication dawns, however, its purposeful intent becomes obvious. The actual first line of the Heart Sutra is:

Avalokiteshvara Bodhisattva, practicing deep Prajna Paramita, clearly saw that all five skandhas are empty, transforming anguish and distress.
Translated by Robert Aitken Roshi of the Diamond Sangha Zen Buddhist Society

The word Dogen adds is, “konshin,” which translates, “whole-body-mind” or “his whole-body-mind.” Although only one word, the significance of this addition is profound. To get this across in English, translators are compelled to get a bit interpretive. Here are the results of two creative attempts to translate Dogen’s altered citation of the line:

When Bodhisattva Avalokiteśvara practices the profound prajnā -pāramitā, the whole body reflects that the five aggregates are totally empty.
Shobogenzo, Maka-hannya-haramitsu, Gudo Nishijima & Mike Cross

When Avalokiteśvara Bodhisattva practices the perfection of profound wisdom, his whole body is the five skandhas, all luminously seen as empty.
Shobogenzo, Maka-hannya-haramitsu, Hee-Jin Kim (Flowers of Emptiness, p.61)

“Five skandhas” (or aggregates) is a traditional Buddhist term for the elements that constitute the whole body-mind of a human being. To “reflect” or “luminously see” means to clearly see the truth of something, to experientially verify. The meaning of ‘prajna’ varies widely, generally connoting ‘wisdom,’ ‘intuitive insight,’ etc.; as “prajna-paramita,” the wisdom or insight of prajna is ‘perfect wisdom’ (i.e. the wisdom of emptiness).

[Note: The five skandhas are: form, sensation, conception, volition, and consciousness. As characteristic of Buddhist categorizations, each of the five skandhas is interdependent with all and each of the other five skandhas. What is true of one is true of all five. Accordingly, Zen/Buddhist expressions frequently employ ‘form’ as an abbreviation for all five skandhas; for that matter, ‘form’ is often employed as an abbreviation for any and all phenomena.]

In his commentary Dogen immediately follows his (altered) citation of the first line of the Heart Sutra with an expression presenting the reasoning (dori) of the Heart Sutra:

The five skandhas are form, feeling, conception, volition, and consciousness, which are the five modes of wisdom. The luminous seeing is itself wisdom.
Shobogenzo, Maka-hannya-haramitsu, Hee-Jin Kim (Flowers of Emptiness, p.61)

‘The luminous seeing is itself wisdom’ – the actual, particular manifest form or activity (i.e. dharma; thing, being, or event) of ‘luminous seeing’ is prajna itself, the reality of perfect wisdom. Hee-Jin Kim clearly articulates the implications of Dogen’s assertion thus:

Avalokitesvara and wisdom are not the observer and the observed, but one reality. The luminous vision then is the working of Avalokitesvara/wisdom. Avalokitesvara sees Avalokitesvara; wisdom enacts wisdom. This reflexive mode of thinking comes from “practicing the perfection of profound wisdom.”
Hee-Jin Kim, Flowers of Emptiness, p.63 (note 5 to the translation of Shobogenzo, Maka-hannya-haramitsu)

It goes without saying that when Dogen says, “clear seeing” he means right-understanding and right-views as well as accurate perception. Shobogenzo, in harmony with all the great Zen classics, frequently urges us to remain mindful of the fact that truly actualizing Buddhist liberation requires more than simply hearing, or even understanding the authentic teachings. The ‘clear seeing’ of practice-enlightenment is a process not a product, an activity not a resolution. Of course the Zen/Buddhist teachings have to be deeply and carefully studied, learned, and accurately understood, but accurate understanding is ineffectual without experiential verification (assimilation and application). Avalokitesvara ‘practices prajna-paramita’ by actively engaging in the ever-advancing process of ‘practicing prajna-paramita’ – liberation is not a fixed-form or static-state, but a flowing-form or continuous-activity of study, practice, and verification. Anyone can come to accurately understand authentic teachings, but only experiential verification can actualize authentic liberation. Next, Dogen elucidates these implications in relation to the key expression of the Heart Sutra, “Form is emptiness, emptiness is form.”

When this meaning is propounded in concrete expression, it is said: “Form is emptiness, emptiness is form.” That is, form is form, emptiness is emptiness. [This principle applies to] all things and all phenomena.
Shobogenzo, Maka-hannya-haramitsu, Hee-Jin Kim (Flowers of Emptiness, p.61)

When Avalokitesvara clearly sees Avalokitesvara is empty, Avalokitesvara clearly sees his/her body-mind (i.e. form) is emptiness itself – ‘form is emptiness.’ When Avalokitesvara clearly sees emptiness is Avalokitesvara, Avalokitesvara clearly sees emptiness is his/her body-mind (i.e. form) itself – ‘emptiness is form.’ Dogen points out that in light of the reasoning (dori) here, the Heart Sutra’s expression, “Form is emptiness, emptiness is form,” leads to the same conclusion arrived at by the methodology of the Diamond Sutra, namely, that “form is form, emptiness is emptiness” and that this applies to all the myriad dharmas.

Here it is worth noticing that for there to be any experience of one’s form (body-mind) as empty necessarily requires one to have/be a form. Hence, it is inevitable that any and every actual experience (epistemological encounter, realization, verification, etc.) of emptiness is and must also be an actual experience of (epistemological encounter with) form. To clearly see, one must have/be a form with the capacity to clearly see – form must be real form. Also, to clearly see the emptiness of one’s form can only occur if one’s form is truly empty – emptiness must be real emptiness.

This is the ultimate point of the Heart Sutra’s expression, “Form is emptiness; emptiness is form.” The import being the interdependence of emptiness and form; the reality (experience, existence, appearance) of form is only possible (meaningful, significant, valid) because of the reality of emptiness and the reality of emptiness is only possible because of the reality of form. Form is experienced when/as/by emptiness not-experienced; emptiness is experienced when/as/by form not-experienced. When/where form is, emptiness is-not; when/where emptiness is, form is-not. As Dr. Kim puts it:

When form is verified, emptiness is “shadowed,” and there is nothing but form: “form is form.” The same holds true of emptiness: “emptiness is emptiness.”
Hee-Jin Kim, Flowers of Emptiness, p.64 (note 7 to the translation of Shobogenzo, Maka-hannya-haramitsu)

This means the reality (true nature) of form is inclusive of the presence of emptiness (as “shadowed”); if not for the (“shadowed”) presence of emptiness, form could not appear. Likewise, the reality of emptiness is inclusive of the presence of form. This explains the emphasis of Zen/Buddhist expressions on the universal quality of emptiness (e.g. all things are essentially empty; emptiness is the true nature of all things, etc.). For only by being clearly aware of this universal quality of reality can we accurately discern and adequately treat any particular dharma (thing, being, or event). To think, speak, or act on a particular dharma without discerning the (“shadowed”) ‘presence’ of emptiness upon which it depends (thus demonstrates), is to think, speak, or act on a biased (i.e. one-sided; deluded) view. Any thought, word, or deed that fails to account for the emptiness of form not only demonstrates delusion about emptiness, but also delusion about form.

After emphasizing that the ultimate principle of the doctrine of emptiness is that form is form, and emptiness is emptiness, the Maka-hannya-haramitsu fascicle underscores that this principle applies to all the myriad dharmas by explicitly identifying a large array of particular aspects and elements as ‘instances’ of ‘prajna-paramita’ or ‘prajna itself.’

They are hundreds of things, and myriad phenomena. Twelve instances of prajnāpāramitā are the twelve entrances [of sense perception]. There are also eighteen instances of prajnā. They are eyes, ears, nose, tongue, body, and mind; sights, sounds, smells, tastes, sensations, and properties; plus the consciousnesses of eyes, ears, nose, tongue, body, and mind. There are a further four instances of prajnā. They are suffering, accumulation, cessation, and the Way. There are a further six instances of prajnā. They are giving, pure [observance of] precepts, patience, diligence, meditation, and prajnā [itself]. One further instance of prajnāpāramitā is realized as the present moment. It is the state of anuttara samyaksaṃbodhi. There are three further instances of prajnāpāramitā. They are past, present, and future. There are six further instances of prajnā. They are earth, water, fire, wind, space, and consciousness. And there are a further four instances of prajnā that are constantly practiced in everyday life: they are walking, standing, sitting, and lying down.
Shobogenzo, Maka-hannya-haramitsu, Gudo Nishijima & Mike Cross

This intentional dwelling on various and particular instances of reality further stresses the importance of understanding that form and emptiness are nondual, not identical. The doctrine of emptiness should not be understood as meaning that emptiness amounts to form or that form is reducible to emptiness. Nonduality denotes unity, not uniformity; emptiness and form are interdependent not indistinguishable. To raise one is to raise both; to eliminate one is to eliminate both – the term ‘both’ is key here. Emptiness cannot reciprocate or coordinate together with emptiness; form cannot cooperate or work in unison with form. ‘Both’ means the reality of form is contingent on the reality of emptiness; the reality of emptiness is dependent on the reality of form. To ‘clearly see’ this and therefore to enact it in our everyday conduct is ‘prajna itself.’

Because dharmas (form/emptiness units) are ‘what’ we clearly see (i.e. experience) as well as ‘the means’ whereby we clearly see, dharmas are ‘clear seeing’ itself, which is, as Dogen asserts, ‘prajna itself.’ One’s true body-mind is identical to the actual dharmas one experiences, and the dharmas one experiences are one’s true body-mind (form/emptiness). This principle applies to all dharmas. Thus, the ‘form’ of each and all the myriad dharmas are us seeing prajna, prajna seeing us, prajna seeing prajna, us seeing us, seeing seeing seeing, prajna prajna-ing prajna, us us-ing us. This is the reason (dori) informing Dogen’s expression:

“Form is emptiness, emptiness is form.” That is, form is form, emptiness is emptiness.
Shobogenzo, Maka-hannya-haramitsu, Hee-Jin Kim (Flowers of Emptiness, p.61)

Dogen’s (altered) citation of the Heart Sutra followed by the series of affirmative expressions on the nature of the self, the world, and the myriad dharmas presents (makes present) a glimpse of the grand vision of Shobogenzo. Here, in the first fascicle explicitly composed for Shobogenzo, the common thread that binds together and runs throughout the whole of Dogen’s masterpiece is prominent. That thread is the reason (dori) of the nonduality of duality, and the duality of nonduality. In short, experience, existence, and liberation (epistemology, ontology, and soteriology) are nondual; the experience of clear seeing, the existence of prajna, and the actualization of liberation are three, but are not three different things. The nature and dynamics of the actualization of the universe (genjokoan) advanced by the nonduality of experience, existence, and liberation is creatively brought into relief i from a variety of perspectives throughout Shobogenzo. To clearly see is to be, thus to clearly see liberation (Buddhahood, enlightenment) is to be liberation – more precisely, the continuous activity of seeing Buddha (kenbutsu) is the continuous activity of becoming Buddha (gyobutsu). My life is what I clearly see, what I clearly see is my life.

So life is what I am making it, and I am what life is making me.
Shobogenzo, Zenki, Gudo Nishijima & Mike Cross

With this we come to a point where we can appreciate the full significance of the passage that serves as the pivot of Dogen’s Maka-hannya-haramitsu:

In the order of Śākyamuni Tathāgata there is a bhikṣu who secretly thinks, “I shall bow in veneration of the profound prajnāpāramitā. Although in this state there is no appearance and disappearance of real dharmas, there are still understandable explanations of all precepts, all balanced states, all kinds of wisdom, all kinds of liberation, and all views. There are also understandable explanations of the fruit of one who has entered the stream, the fruit of [being subject to] one return, the fruit of [not being subject to] returning, and the fruit of the arhat. There are also understandable explanations of [people of] independent awakening, and [people of] bodhi. There are also understandable explanations of the supreme right and balanced state of bodhi. There are also understandable explanations of the treasures of Buddha, Dharma, and Sangha. There are also understandable explanations of turning the wonderful Dharma wheel to save sentient beings.” The Buddha, knowing the bhikṣu’s mind, tells him, “This is how it is. This is how it is. The profound prajnāpāramitā is too subtle and fine to fathom.”
Shobogenzo, Maka-hannya-haramitsu, Gudo Nishijima & Mike Cross

The thoughts of this monk (bhiksu) go to the heart of the reason of emptiness demonstrated by the vision of Shobogenzo; because there is no self and there is no other in the true multitudinous-oneness of emptiness, true, effective, understandable teachings exist. Unlike those enamored by and attached to the sublime power of the ‘deconstructive’ capacity of emptiness (i.e. ‘form is emptiness’), this monk strives on, advancing to see through to the ‘reconstructive’ capacity of emptiness (i.e. ‘form is form, emptiness is emptiness’). Thus, the Buddha says; “This is how it is. This is how it is.”

There are understandable explanations. There are understandable explanations of precepts, balanced states, wisdom, and liberation. The no-self of emptiness does not mean that things are not real, that distinctions are illusory, or that the reality of things is other than the appearance of things. Zen doctrine and methodology exists and is effective because particular Zen ancestors learned, understood, verified, and actualized understandable explanations of reality. Commenting on the monk’s thought that, “Although in this state there is no appearance and disappearance of real dharmas, there are still understandable explanations,” Dogen says:

The bhikṣu’s “secretly working concrete mind” at this moment is, in the state of bowing in veneration of real dharmas, prajnā itself—whether or not [real dharmas] are without appearance and disappearance—and this is a “venerative bow” itself. Just at this moment of bowing in veneration, prajnā is realized as explanations that can be understood: [explanations] from “precepts, balance, and wisdom,” to “saving sentient beings,” and so on. This state is described as being without. Explanations of the state of “being without” can thus be understood. Such is the profound, subtle, unfathomable prajnā pāramitā.
Shobogenzo, Maka-hannya-haramitsu, Gudo Nishijima & Mike Cross

The very act of this monk’s “bowing in veneration” is a manifestation of prajna made real (realized) by and as “explanations that can be understood.” At the very moment a Zen practitioner encounters an explanation (say, in reading Shobogenzo) and thereby comes to an accurate understanding (i.e. is enlightened to a truth), an instance (i.e. dharma; a spatial-temporal form) of prajna is actualized (made actual). This newborn dharma is empty – the ‘explanation’ (Dogen’s writing), the ‘encounter’ (the practitioner’s reading), the ‘understanding’ (the practitioner’s insight), its ‘particular significance’ (the dharma’s truth), its ‘influence’ (on the practitioner’s conduct), and its ‘effect’ (on the world through the practitioner’s conduct) are not its ‘self’, nor are they ‘other than itself.’ Thus prajna is realized (made real). “This state” – in/of/as prajna being realized – is described as emptiness (i.e. mu: ‘being without’).

Following the illumination of this monks “secretly working concrete mind” Dogen goes on to underscore how actual, concrete instances of prajna are realized in the everyday world through the body-mind’s of sentient beings. To do so, Dogen makes creative use of a traditional story from Buddhist mythology wherein one of the gods (Indra) asks Subhuti how the profound doctrine of emptiness (prajna-paramita) should be studied and learned. The Buddha’s disciple responds by saying it should be studied as ‘emptiness’ (koku; space). At this point Dogen states:

So studying prajnā is space itself. Space is the study of prajnā.
Shobogenzo, Maka-hannya-haramitsu, Gudo Nishijima & Mike Cross

Apparently not totally confident in the reliability of this assertion, the god asks:

“World-honored One! When good sons and daughters receive and retain, read and recite, think reasonably about, and expound to others this profound prajnāpāramitā that you have preached, how should I guard it? My only desire, World-honored One, is that you will show me compassion and teach me.”
Then the venerable monk Subhūti says to the god Indra, “Kauśika! Do you see something that you must guard, or not?”
The god Indra says, “No, Virtuous One, I do not see anything here that I must guard.”
Subhūti says, “Kauśika! When good sons and daughters abide in the profound prajnāpāramitā as thus preached, they are just guarding it. When good sons and daughters abide in the profound prajnāpāramitā as thus preached, they never stray. Remember, even if all human and nonhuman beings were looking for an opportunity to harm them, in the end it would be impossible. Kauśika! If you want to guard the bodhisattvas who abide in the profound prajnāpāramitā as thus preached, it is no different from wanting to guard space.”
Shobogenzo, Maka-hannya-haramitsu, Gudo Nishijima & Mike Cross

Dogen goes on to emphasize the significance of this exchange by summarizing and clarifying the main points:

Remember, to receive and retain, to read and recite, and to think reasonably about [prajnā] are just to guard prajnā. And to want to guard it is to receive and retain it, to read and recite it, and so on.
Shobogenzo, Maka-hannya-haramitsu, Gudo Nishijima & Mike Cross

To conclude this survey of Dogen’s treatment of emptiness, I turn to Hee-Jin Kim’s translation and concluding notes of Dogen’s final passage, the first line of which Kim translates:

Therefore is Buddha the Holy One perfect wisdom.
Shobogenzo, Maka-hannya-haramitsu, Hee-Jin Kim (Flowers of Emptiness, p.62)

Dr. Kim points out in a note on this line:

In this paragraph Dogen expounds the nonduality of the Buddha and wisdom, of the personal and impersonal. He even boldly admonishes his disciples to honor and revere perfect wisdom.
Shobogenzo, Maka-hannya-haramitsu, Hee-Jin Kim (Flowers of Emptiness, p.66)

The translation of the rest of the final passage runs:

Perfect wisdom is all dharmas. These dharmas are empty in their form – no arising or perishing, no impurity or purity, no increasing or decreasing. The realization of this perfect wisdom is the realization of Buddha the Holy One. Inquire and practice: To honor and revere [perfect wisdom] is indeed to respectfully meet and serve Buddha the Holy One; to meet and serve him is none other than to be Buddha the Holy One.
Shobogenzo, Maka-hannya-haramitsu, Hee-Jin Kim (Flowers of Emptiness, pp.62-63)

Dr. Kim’s note on this final passage reads:

The very act of respectfully meeting and serving is the buddha. This is in accordance with the notion of the enactment-buddha (gyobutsu), wherein enactment and buddha are one.
Shobogenzo, Maka-hannya-haramitsu, Hee-Jin Kim (Flowers of Emptiness, p.66)